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RAID (/ r eɪ d /; redundant array of inexpensive disks or redundant array of independent disks) [1] [2] is a data storage virtualization technology that combines multiple physical data storage components into one or more logical units for the purposes of data redundancy, performance improvement, or both.
Diagram of a RAID 1 setup. RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks; a classic RAID 1 mirrored pair contains two disks.This configuration offers no parity, striping, or spanning of disk space across multiple disks, since the data is mirrored on all disks belonging to the array, and the array can only be as big as the smallest member disk.
Nested RAID levels, also known as hybrid RAID, combine two or more of the standard RAID levels (where "RAID" stands for "redundant array of independent disks" or "redundant array of inexpensive disks") to gain performance, additional redundancy or both, as a result of combining properties of different standard RAID layouts.
RAID stands for redundant array of independent disks (or, formerly, redundant array of inexpensive disks). RAID levels may refer to: Standard RAID levels, all the RAID configurations defined in the Common RAID Disk Drive Format standard, which is maintained by the Storage Networking Industry Association
A Redundant Array of Inexpensive Servers (RAIS) or Redundant Array of Independent Nodes (RAIN) is the use of multiple servers to maintain service if one server fails. This is similar in concept to how RAID turns a cluster of ordinary disks into a single block device.
HP EVA4400 storage array, consisting of 2U controller enclosure (top) and 4 2U disk shelves. A disk array is a disk storage system which contains multiple disk drives. [1] It is differentiated from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID, deduplication, encryption and virtualization.
In the adjacent diagram, data are concatenated from the end of disk 0 (block A63) to the beginning of disk 1 (block A64); end of disk 1 (block A91) to the beginning of disk 2 (block A92). If RAID 0 were used, then disk 0 and disk 2 would be truncated to 28 blocks, the size of the smallest disk in the array (disk 1) for a total size of 84 blocks.
Both drums and data cells have disappeared as products, so DASD remains as a synonym of disk, flash and optical devices. Modern DASD used in mainframes only very rarely consist of single disk-drives. Most commonly "DASD" means large disk arrays utilizing RAID schemes. Current devices emulate CKD on FBA hardware.